2015 Passing Plus-Minus

by Scott Kacsmar

Completion percentage has often been a simpleton's approach to quantifying a quarterback's accuracy. While we would still have to get some pretty advanced software to perfectly measure accuracy, we can do a better job of things just with game charting. For starters, not every pass is actually aimed with the intention of a completion. By breaking down every incompletion into classes, we can account for passes thrown away as well as drops.

Then there is the significance of how far the pass was thrown. If a quarterback wanted to complete 75 percent of his passes in a season, he could definitely hit that mark, but it would likely come at the expense of a productive offense. Since 2006, aimed passes thrown to receivers behind the line of scrimmage have been completed 87.3 percent of the time. Aimed passes that travel exactly 10 yards beyond the line of scrimmage are completed 59.2 percent of the time. At 20 yards, that rate dips to 44.7 percent.

It is also worth noting which field direction the pass was thrown: left, middle, or right. A 4-yard pass to a slot receiver coming over the middle is actually still a shorter throw than a 4-yard pass thrown to a curling wide receiver on the outside. On average, the further the ball has to travel, the less likely it is to get there accurately. We broke down passes thrown 1 to 20 yards downfield over the last decade by the three directions, and found that the middle is very advantageous.

Throws to the left and right are hardly distinguishable from one another, but once you get to 3-yard throws, the middle starts to separate. At 12 yards and deeper, throws to the middle are completed about 10 percent more often. We could probably do a whole piece on direction, but much of what's going on here is that a higher rate of passes over the middle (45.9 percent) go to running backs and tight ends than those thrown towards the left (36.3 percent) or right (40.5 percent). These positions historically have higher catch rates due to a closer playing proximity to the quarterback, hence shorter throws. They also get a lot of matchups with linebackers and safeties instead of cornerbacks, which usually are the athletes best suited for tighter coverage. Good quarterbacks can really exploit the seam passes in windows between the linebackers and safeties, and most dump-off passes also get checked down to the middle.

So we want a stat that will account for where the pass was thrown, how far it was thrown, and what the down-and-distance situation was. The end result is passing plus-minus. We have looked at receiving plus-minus in the past; this is the same concept, but for quarterbacks. Passing plus-minus estimates how many passes a quarterback completed compared to what an average quarterback would have completed, given the location of those passes. It does not consider passes listed as "Thrown Away," "Tipped at Line," or "Quarterback Hit in Motion." Player performance is compared to a historical baseline of how often a pass is completed based on the pass distance, the distance required for a first down, and whether it is on the left, middle, or right side of the field. Note that plus-minus is not scaled to a player’s total attempts.

Passing Plus-Minus: Top and Bottom Seasons

Since we are sitting on 10 seasons of data for this, and have never really published a formal study on the stat for quarterbacks, let's look at the top seasons since 2006. These are the 45 seasons to finish with at least a plus-20. (For the rest of the article we will express the numbers with a + or - sign.)

Well, Drew Brees should love this stat. He only has four of the top five seasons. It's true that volume helps a lot here, but when you have volume and you are probably the most accurate passer in the league, you're going to dominate plus-minus.

This list is pretty top-heavy, with 16 quarterbacks (including most of the usual suspects) comprising the top 45. David Carr sticks out like a sore thumb for his 2006 season with Houston, but he did complete 68.3 percent of his passes that season and they were not all screens. You can also see Teddy Bridgewater and Kirk Cousins cracked this list for their 2015 performances. Time will tell if they develop into consistently solid quarterbacks, or if they belong in Carr's tier as one-offs.

Plus-minus does a good job of picking out bad quarterbacks with major accuracy issues. Here are the 22 seasons to finish at -20 or worse.

Not a lot of good quarterback play here. Brett Favre struggled in his first season with Mike McCarthy, but did rebound in 2007. Eli Manning actually won his first Super Bowl after a rather weak regular-season performance. Andrew Luck's rookie season was inefficient, but still one of the more impressive examples of a quarterback carrying a team. The rest of the list is largely the other group of usual suspects from the last decade. Josh Freeman somehow managed to sink this low in 2013 despite attempting just 137 passes. Derek Anderson may have tricked a few people with his 29-touchdown 2007 performance in Cleveland, but even that season was a -20.3, and his three appearances are tied with Mark Sanchez for the most on the list. Blake Bortles will hope his rookie season isn't a sign of things to come like Blaine Gabbert's 2011 was for Jacksonville, but fortunately 2015 looks to be a step in the right direction.

2015 Passing Plus-Minus

These results are for the 2015 passers with at least 200 pass attempts. Again, the total number of passes will differ from the NFL total due to the removal of certain passes. To help express plus-minus as a rate stat, C%+ is also included.

Last season was a tough one for the quarterbacks we are used to seeing dominate such stats. In his prime, Peyton Manning was the top quarterback in plus-minus. He slipped to ninth in 2014, and that decline only continued with his first negative season in 2015, his swansong. Tom Brady had his second negative season in the last three years. Aaron Rodgers was at +15.0 or higher in each of the previous seven seasons, but sunk to -11.9 last year. Yes, Jordy Nelson matters when you consider Rodgers was +56.8 in his career on targets to Nelson. However, Rodgers was +28.0 to Randall Cobb from 2011-14 before a -2.2 connection in 2015. Davante Adams' -7.1 is by far the worst plus-minus season for any of Rodgers' targets in his career.

Some quarterbacks were at their best in 2015, or at least gave the illusion of it. Russell Wilson's league-leading plus-minus of +27.4 was really built on the +16.7 he had when he went on an incredible run in the last seven games of the season. Ben Roethlisberger has had much better seasons throwing touchdowns and interceptions, but he may have been at his physical best throwing the ball in 2015 with a career-high +26.2. We lack 2005 data, but Carson Palmer's 2015 is his best season on record now. You might have thought the same could be said for MVP Cam Newton, but his 2013 season actually had a higher plus-minus at +6.2. Andy Dalton had his best season last year, though he has usually been middle of the pack in plus-minus, ranking 12th to 16th every year except for his rookie season. Matthew Stafford had his second positive season, and yes, things were better in nine games with offensive coordinator Jim Bob Cooter (+4.8) than they were with the fired Joe Lombardi (+0.9).

Teddy Bridgewater is likely to be a focal point in several of our quarterback studies this year. He did not fare well in Expected Failed Completions, looking like one of the league's more dink-and-dunk passers. But when it comes to plus-minus, Bridgewater has been quite good, ranking 15th as a rookie and fifth this year. Even on passes thrown 10-plus yards, Bridgewater still ranked 10th in plus-minus (+5.2) in 2015. While Bortles and Derek Carr each threw more touchdowns in 2015 than Bridgewater has in two seasons, the gap in passing efficiency is definitely in Bridgewater's favor. When we get around to looking at performance with pass pressure in 2015, you may be even more impressed by Bridgewater.

Say what you will about Chip Kelly's offense in the NFL, but he has helped make the job of completing passes easier on his quarterbacks. Nick Foles was +17.2 in his great 2013 season, but finished dead last at -24.0 with the Rams last year. Sam Bradford was -25.3 in his time with the Rams, but had his first positive season with the Eagles in 2015. Mark Sanchez's C%+ was -4.6% with the Jets, but improved to -1.4% (which, granted, is still not good) in two years with Philadelphia. Colin Kaepernick's plus-minus has gotten worse each season, but Kelly should be able to help him, or (gulp) Blaine Gabbert in San Francisco.

Drop-Adjusted Passing Plus-Minus

Since plus-minus is all about getting the pass completed, and has nothing to do with what happens after the catch, we can make a clean adjustment for dropped passes. In 2010, his last playing season with the Colts, Peyton Manning finished fourth in plus-minus at +18.3. He was credited with 48 dropped passes, which were worth -31.1 plus-minus. In adjusting his plus-minus for drops, we do not simply add the 31.1 to his season total; we add the difference between the drops (48) and the plus-minus (31.1), which is +16.9, the highest of any season in the last decade. Adding +16.9 to Manning's statistics that season results in a drop-adjusted plus-minus of +35.2, good for third in 2010. Manning ranked first or third in every season he played from 2006 to 2013.

Manning and Brees have led the league four times each in drop-adjusted plus-minus since 2006. Tom Brady (2007) and Wilson (2015) are the only other quarterbacks to lead the league. Brees' 2011 season is still the highest (+57.1), and Manning's 2009 season has the highest adjusted C%+ (+9.8%).

This table looks at 2015 again with drop-adjusted plus-minus. Do we dare go for another acronym with DA +/-?

While the Colts led the league in drops in 2014, they did not drop many last season when Andrew Luck was playing, which drops him from 29th to 34th in DA +/-, the biggest fall for any quarterback. Brady had the highest rise, going from 22nd to 17th. But 31 of the 36 passers stayed within two spots of their regular plus-minus ranking.

Finally, here is the full leaderboard since 2006 in DA +/- (min. 1,000 passes). This only includes the regular season.